The invention relates to an apparatus comprising a circuit which supplies an output signal in response to an input signal, means for changing values of said response by means of at least one control signal, calculation means for determining second pairs of response values/control signal values on the basis of an approximation of first pairs of response values/control signal values issuing from the circuit.
The invention also relates to a coding device intended for use in conjunction with such an apparatus and a method of determining said second pairs on the basis of an approximation of a series of first pairs.
Electrical or electronic circuits are known whose responses are controllable by means of devices having a property which can be varied by means of a control signal. For example, it is known to use variable capacitance diodes which have the property that their capacitance is variable by applying a variable voltage across the diode. By means of the capacitance/voltage variations it is possible to tune various electrical circuits such as oscillators or to control pass bands of filters. By means of variable conductance elements it is likewise possible to vary the gain factors of amplifiers.
Similar control mechanisms can be obtained with other elements such as gyrators, transistors or composite devices such as operational amplifiers or transconductance amplifiers.
Such units can be used in apparatuses such as television receivers, radio receivers, recording equipment and the like.
For these uses it may be desirable to have a plurality of control conditions which can be selected individually. Implementation of these control conditions should be possible with rapid procedures and with minimal hardware.
The document EP 0,147,518 discloses a tuning method for frequency selective circuits and a circuit for carrying out this method. These selective circuits, which include variable capacitance diodes, are incorporated in a tuner used, for example, in a television receiver or a radio receiver. The circuit comprises a local oscillator which serves to tune said selective circuits, generally in the factory, to the frequencies of given channels by varying the control signals applied to said diodes.
The method consists of setting the local oscillator to a frequency corresponding to a given channel, and subsequently varying the control signal voltages applied to the capacitance diodes so as to obtain an optimum alignment of the high-frequency circuit to said channel frequency. The values of the control signals applied to the capacitance diodes are then stored. These values can also be stored as deviations with respect to a corresponding voltage applied to the local oscillator, in order to reduce the capacity of the storage memory.
The alignment is controlled by an external computer. The control signals thus determined are stored in a memory in order to be read out when a selective circuit is to be tuned to a frequency of a given channel. If no value of the control signal has been stored for the desired frequency an internal computer can perform a procedure of linear interpolation between two adjacent stored values of the control signal. Each time that the channel is changed the user thus changes a control signal applied to the capacitance diode(s), which results in the desired tuning.
In order not to degrade the accuracy of the obtained tuning it is necessary to store almost as many set-point values as there are channels to be selected. Also, the linear interpolation procedure may lead to significant errors. The large number of setpoint values to be stored requires the use of a memory of such a size that the costs are no longer negligible. The size of this memory is therefore a drawback.